1. Field of the Invention
The present invention relates to a novel polymerizable main chain type liquid crystalline polyester, a liquid crystalline composition containing such a main chain type liquid crystalline polyester, a method for producing a liquid crystal film obtained by polymerizing such a liquid crystalline composition, an optical film produced by such a method, and a display equipped with such an optical film.
2. Background Information
Studies and developments have been actively done to utilize liquid crystalline compounds as optical materials, and many of the compounds have already been put in practical use. When a liquid crystalline compound is used as an optical material, it is requisite to retain the structure of the liquid crystal having been aligned and fixed, under practical service conditions. There have been proposed methods for fixing a liquid crystal structure wherein a polymerizable liquid crystalline compound is used, wherein a polymeric liquid crystalline substance is used, and wherein a polymeric liquid crystalline substance having a polymerizable reactive group is used.
Published Japanese translation of PCT Application Nos. 11-513019 and 11-513360 disclose methods wherein polymerizable liquid crystalline compounds are used. The polymerizable liquid crystalline compounds are low molecular weight liquid crystalline compounds containing two or three benzene rings bonded via ester groups, as a mesogen. In the case of using such low molecular weight liquid crystalline compounds as materials of an optical film, a method is possibly used wherein the compounds are heat-melted and then coated in a liquid crystal state over a film substrate. However, it is difficult to obtain a uniform film with a high accuracy in thickness by this method. Furthermore, in the case of using the compound in the form of a solution, there frequently arises a difficulty in coating such a solution over a film due to the low solution viscosity. Therefore, in order to produce a self-standing type optical film, the above-mentioned publications propose methods wherein a glass cell after a liquid crystal material is filled thereinto is subjected to heating and ultraviolet irradiation so as to cure the material, and the glass substrates are removed from the cured material. However, these methods are rather complicated, comparing with a method wherein a liquid crystal material is coated over a film substrate.
Japanese Patent Laid-Open Publication No. 11-158258 discloses a method using a polymeric liquid crystalline substance which is a liquid crystalline polyester with excellent properties to retain the liquid crystal orientation. However, as a result of the widespread of mobile devices, an optical film comprised of such a liquid crystalline polyester has been demanded to have properties to retain the liquid crystal orientation under more sever practical use conditions and more excellent mechanical strength as well.
A method using a polymeric liquid crystalline substance having a polymerizable reactive group is disclosed in Japanese Patent Laid-Open Publication No. 9-003454. The former proposes a method wherein a polymerizable reactive group is introduced into the polymeric main chain, and the latter proposes a method wherein monomer units having a polymerizable reactive group are introduced into the side chains. However, since in either of these methods the liquid crystallinity of the material used is decreased due to the introduction of polymerizable reactive groups, there is a limit to the amount thereof and thus sufficient mechanical strength can not be obtained. Therefore, alternative methods have been demanded.
The object of the present invention is to provide a polymerizable main chain type liquid crystalline polyester with an excellent capability to retain the liquid crystal orientation after having been aligned and fixed and excellent mechanical strength and also an optical film obtained from the liquid crystalline polyester.